The present invention relates generally to differential driver circuits, and more specifically to a high-speed multi-channel differential driver circuit that is LVDS compatible.
In recent years, Low Voltage Differential Signaling (LVDS) technology has been increasingly employed in high-speed data transmission systems. In general, LVDS technology is a signaling method used for high-speed low-power data transmission over transmission media such as Printed Circuit Board (PCB) traces, backplanes, and cables. The LVDS signaling method, which conforms to the TIA/EIA-644 standard, uses low voltage levels (e.g., less than 5 volts) to allow operation with decreased power supply levels, to reduce power consumption, and to increase switching speeds.
According to the TIA/EIA-644 standard, the input leakage current for an LVDS-compatible circuit is specified to be less than 20 μA, which can be problematic for high-speed multi-channel differential driver circuits such as high-speed multi-channel repeaters. This is because such high-speed repeaters typically include a multiplexor, which may be placed at the front of the signal chain within the repeater circuit. By placing the multiplexor at the front of the signal chain, the high-speed repeater can be configured such that each driver within the circuit is connected to only one receiver, thereby avoiding problems related to internal loading and assuring that consistent AC performance is achieved.
However, such front-multiplexed multi-channel repeater circuits have drawbacks in that high input leakage can occur under certain operating conditions. For example, the multiplexor of the conventional front-multiplexed repeater may include a plurality of transmission gates. Because of the PMOS transistor back-gate diode-to-power supply current paths within the transmission gates, input leakage current levels can increase when an input voltage of the multiplexor exceeds the supply voltage, thereby making it difficult to meet the input leakage requirement called out in the TIA/EIA-644 specification.
It would therefore be desirable to have a high-speed multi-channel differential driver circuit that conforms to the TIA/EIA-644 specification, and avoids the drawbacks of the above-described conventional front-multiplexed multi-channel repeater.